The modern molecular clock

The discovery of the molecular clock - a relatively constant rate of molecular evolution-provided an insight into the mechanisms of molecular evolution, and created one of the most useful new tools in biology. The unexpected constancy of rate was explained by assuming that most changes to genes are effectively neutral. Theory predicts several sources of variation in the rate of molecular evolution, However, even an approximate clock allows time estimates of events in evolutionary history, which provides a method for testing a wide range of biological hypotheses ranging from the origins of the animal kingdom to the emergence of new viral epidemics

Cryo-Crystallography: Diffraction at Low Temperature and More

This chapter comments on the motivations and the methods of crystallographic studies at low temperature. Cry-crystallography is a brunch of Crystallography, a science that is too often confused with a technique. On the other hand, the scientific background to study crystal phases at low temperature is here provided, together with a survey of many possible techniques that provide complementary or supplementary information. Several applications are discussed, in particular in relation with highly accurate studies like electron density determination or phase transition mechanisms. © 2011 Springer-Verlag Berlin-Heidelberg